"Iran knows how to get to the table with US," Bush told reporters during a visit to Estonia. "And that is to do that which they said they would do, which is verifiably suspend their enricmen programmes."
The US alleges Iran is secretly developing atomic weapons, though Tehran has repeatedly claimed its programme is for peaceful purposes, including generating electricity.
"The idea of this regime having a nuclear weapon, by which they could blackmail the world, is unacceptable to free nations," Bush said.
Speaking at a news conference before hearing to a NATO summit in neighbouring Latvia later in the day, Bush also accused Iran and Syria of undermining the government in Lebanon.
"That government is being undermined, in my opinion, by extremist forces encouraged out of Syria and Iran," Bush said. He added that a democratic Lebanon "will be a major defeat for those who articulate extremist point of views."